1. Field of the Invention
The present invention relates to a facsimile apparatus and, more particularly, to the control of a reader motor to read an original to be transmitted by a facsimile apparatus.
2. Related Background Art
A conventional facsimile apparatus has not only a main CPU to control the whole apparatus but also a sub CPU to control a reader motor to move a reading original to a reading position. When the motor is rotated in the above construction, a motor trigger command and information indicative of the number of motor steps for the motor trigger are supplied from the main CPU to the sub CPU, thereby rotating the motor.
Such a construction also applies to a facsimile apparatus which has an image memory and in which an image signal which has been read and coded is stored into the image memory at a high speed, namely, a facsimile apparatus having a high speed reading mode.
In case of the high speed reading, it is necessary to set the reading timing to be almost constant and to rotate the reader motor at a high speed.
For this purpose, there is considered a method of rotating the reader motor at a high speed within a pull-out torque by the acceleration control. That is, to rotate the motor at a higher speed within a pull-in torque, it is necessary that a large powerful expensive motor be used in the apparatus. Therefore, such a method is effective in case of providing a small cheap apparatus to the user.
In the above conventional facsimile apparatus, namely, in a facsimile apparatus which has an image memory and stores image data into the image memory at a high speed and, after that, transmits or copies the signal stored in the image memory, that is, performs the high speed reading, and in which the acceleration control of the motor is executed to rotate the reader motor at a high speed and the motor is used in the pull-out torque, it is necessary to issue the motor trigger command from the main CPU to the sub CPU at a high constant speed.
When the motor trigger command is issued, a check is made to see if the motor is busy or not on the basis of the information from the sub CPU and, thereafter, the motor trigger command is issued. Therefore, as the rotational speed of the motor is raised as high as possible, it is necessary to make the timing to check such a motor busy status and the timing to issue the motor trigger command as fast as possible. In the case where the motor trigger timing is deviated by some cause, there occurs a serious problem such that since the motor is used within the pull-out torque, the motor loses synchronism, the original to be transmitted cannot be conveyed, and the same position of the original is permanently read.
Particularly, in a facsimile apparatus which operates in what is called a dual access mode such that while the image is being read at a high speed, another process such as communication, printing of the received image, printing of a communication management report, or the like is also simultaneously executed, a direct memory access (DMA), an interrupting process, or the like to execute a process other than the high speed image reading exerts an influence on the timing of the motor trigger. Among them, the process regarding the communication needs to be executed at a highest priority because the communication transmitting speed and the timing for communication protocol have severely been determined by the standard such as CCITT or the like. Therefore, in case of performing the high speed image reading during the communication, there frequently occurs a problem such that the motor trigger timing is deviated due to the influence by the communication and the motor cannot be rotated at a constant speed within the pull-out torque because of such a timing deviation, so that the motor loses synchronism.